More than 325 million people worldwide have been helped by the more than 155 recombinantly produced polypeptides and peptides (drugs and vaccines) currently approved by the United States Food and Drug Administration. In addition, there are more than 370 biotechnology drug products and vaccines currently in clinical trials targeting more than 200 diseases, including: various cancers, Alzheimer's disease, heart disease, diabetes, multiple sclerosis, AIDS and arthritis. However, development and manufacturing of therapeutically useful polypeptides has been hampered, in large part, by the limitations of the organisms currently used to express these exogenous polypeptides.
Unlike traditional small molecule therapeutic agents, which are produced through classical chemical synthesis, polypeptides are produced and purified from living cells in an inefficient and costly process. To generate large quantities of polypeptides for biotechnology applications, it is typically necessary to express a polypeptide as a “recombinant” product in an organism distinct from the original source (e.g., human polypeptide produced in a bacterial cell). This is necessary because it is often difficult to obtain adequate quantities of polypeptide from native sources. A number of systems have been developed for the expression of polypeptides in bacterial, yeast, insect and animal cells. When practical, bacterial expression systems are ideal because bacteria grow rapidly, bacterial growth medium is inexpensive and less prone to contamination, bacterial physiology is relatively well understood, and several strains of genetically modified bacteria have been developed to produce high-quality, intact recombinant polypeptides.
To express a recombinant polypeptide in a non-native organism, it is generally necessary to optimize the gene sequence. This optimization includes putting the gene under the control of a strong inducible promoter, adding sequences that facilitate purification and increase polypeptide stability, and altering rare codons within the coding sequence. Despite the development of techniques for polypeptide production in bacterial systems, it is still difficult to obtain high-yields of certain polypeptides. This is particularly true when attempting the production of polypeptides from higher organisms such as humans, due to small but significant differences in the structures of human and bacterial genes. A need exists for improved methods for expressing recombinant polypeptide in non-native organisms. The present invention addresses this and other needs.